Interrelations between the P_excess and F_Si/F_cont of cometary dust in the K (a) and red (b) domains, respectively, with Spearman’s rank correlation coefficient (ρ) shown in the upper left of each panel. The meaning of the symbols is the same as in Figs. 1 and 2. Black circles and squares around the comet symbols indicate carbon-rich and silicate-rich comets, respectively, as defined in the main text.